John b



(No Model.) 2 Sheets-Shawl. J.-B. RO0T.

I Screw Propeller.

No. 240,613. Patented Apri'l 26, 1-881.

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N PETLRS. PNDTO-LITHOGRAPNER. WASHINGTON. 0 C,

(No Model.) 2 Sheets-Sheet B. 3001 Screw Propellern, No. 240,613; PatentedApril,26, I881.

UNITED STATES PATENT Curr es.

JOHN B. ROOT, OF PORT CHESTER, NEW YORK.

SC REW-PROPELLER.

SPECIFICATION forming part of Letters Patent No. 240,613, dated April 26, 1881.

Application filed October 9, 1880.

To all whom it may concern:

Be it known that I, JOHN B. R001, of Port Chester, in the county of Westchester and State ofNew York, have invented a new and useful Improvement in the Propulsion of Vessels, of which the following is a specification.

The present invention relates to that class of vessels which are driven through the water by the action of screw-propellers and its principal object is to obtain greater speed with the expenditure of the same amount of power, or the same speed with a less amount of power, as compared with such vessels as at present constructed and operated.

The invention consists in placing the shaft or axis of the propeller or screw in an inclined; position-th at is, inclined downward and backward, or at an angle to the line of movement of the vessel-and at the same time increasing the diametric or propelling area of the screw and decreasing its pitch relatively to the inclination or angle of the shaft.

Although shafts of screw-propellers have generally been attached to vessels so as to lie in a horizontal plane, yet, in some instances, they have been placed in an inclined position, for the purpose of adapting the shaft to the driving machinery of the hull, and perhaps for giving more perfect submergence 0f the screw in the water. In all such cases, however, so far as I am aware, the construction of the screw has been such that the speed of the vessel has been less than the pitch of the screw multiplied by the number of its revolutions, owing to the .slip due to the yielding nature of the water; and I am not aware of any casein which the area of the screw has been increased and at the same time its pitch diminished by reason of such inclination given to the shaft.

I have discovered that by giving the shaft of a screw-propeller a sufficient inclination downward and backward, or at an angle to theline of movementof the vessel, and by increasing the diametric or propelling area of the screw relatively to the inclination or the angle of the shaft, the vessel can be propelled very much farther by a given number of revolutions of the screw than the pitch of'the screw multiplied by the number of its revolutions would call for, provided the shaft were ar-, ranged horizontally in the vertical plane of the keel, as usually applied.

(No model.)

Whenever the shaft of a propeller is placed in an inclined position without increasing the diametric or propelling area of the screw, there will be a greater slip, resulting from the upward action of the screw against the weight of the vessel, whereby an increased thrust is required to give the same forward push upon the vessel,

to the screw in the given time, owing to its increased thrust, than would be required to give the same number of revolutions in the same time if the screw-shaft were horizontal;

but if the pitch of a screw of increased area acting on aninclined shaft is reduced or diminished relatively to the inclination of the shaft, a point is reached at which the same power will give to such screw the same number of revolutionsiin the same time as would be given to a screw of the pitch :and area adapted to a shaft working horizontally and in the vertical plane of the keel. With a screw thus constructed and arranged a greater speed can be attained with the same expenditure of power than with the known constructions of horizontal or inclined screws.

In the drawings, Figure 10 illustrates one method by which to determine the pitch and area of a screw embodying my invention. In

this figure the line a b c 61 represents the line of movement of the vessel, and the part c d (or a b, which is laid off equal to c d) represents the pitch of a screw. adapted to a shaft working horizontally in the fore-and-aft line of the vessel. The curve a 0 d is a half-circle, constructed on 0d, and ac m is the quadrant of a circle, constructed on the radius ac. The angles which the radial lines a o, e c, f c, &c., make with the perpendicular cm represent different degrees of inclination that may be given to the axes of screw-propellers, and each of which, were there no slip, would, with the, proper pitch and area of screw, move the vessel from c to d with a single turn of the shaft, and the ,dotted portion of any one of these lines, as

compared with the line a b, represents approximately the relative pitchwhich thescrewshould as compared with its pitch if its shaft were horizontal and in the fore-and-aft line of the vessel. The diameter of the screw should be increased in approximately the same proportion as the pitch is diminished. A rule, then, for proportioning the pitch and the propelling area of the screw to the inclination of the shaft will be as follows: Ascertain, by the estab lished methods, the area and pitch of a screw on a horizontal shaft, lying in the plane of the keel, which will propel the vessel at a given speed with a given number of revolutions of the screw. If, now, it is desired to incline the shaft at, say, thirty degrees from the perpendicular, ascertain from a diagram constructed on the plan of Fig. 10 the relative length of the dotted radial line on this angle of inclination as compared with the line a I), representing the ascertained pitch of the screw on a horizontal shaft. It will be found to be approximately one-half, and consequently, to secure the best results, the pitch of a screw placed on an inclination of thirty degrees from theperpendicular should be about onehalf that of a screw having its axis horizontal and in the plane of the keel. At the same time the diameter of the screw should be increased in substantially the same ratiothat is, in this case, should be about doubled, which approximately would quadruple its propelling area. The reason for thus increasing the propelling area of the screw as its pitch is reduced is, that the water acted upon by a screw of a given pitch will be propelled backward with double the velocity imparted by a screw of one-half such pitch; and as the resistance is as the square of the velocity, it follows that, in order to avoid an increase of slip, the diameter of the propelling-surface of the screw should be increased as the pitch is diminished.

The same rule will apply, mutatis mutandis, to any other angle of inclination at which it may be desired to place the shaft.

While it is considered that the above furnishes a convenient and approximately accurate rule for determining the relation of the area and pitch of the screw to the inclination or angle of the shaft, in order to produce the best results, it is doubtless true that many other methods or rules may be employed to obtain the same result, and it is not intended to limit the invention by any special rule or method of determination in this respect; nor is the invention limited to the exact proportions of inclination of shaft, propelling area, and pitch of screw suggested above as producing the best results. The endeavor has been to state the general principle of the invention, and it is probable that varied conditions and requirements of construction and use will often call for variations from the proportions given, which, under ordinary circumstances, would give the best results.

The advantages resulting from the abovedescribed construction and arrangement of screw-propellers are, that the resistance of the vessel is diminished by the lifting action of the screw; also, that the loss from slip is diminished by reducing the pitch of the screw.

By diametric or propellingarea, as herein used, is understood the area of the circle described by the blades in their revolution, and not simply the area of the blades themselves; and by the term pitch, as herein used, is meant the distance along the line of the shaft that a blade of the screw would travel at one revolution if moving without slip.

The same effect which is produced by reducing or diminishing the pitch of a screw, as above explained, may be obtained, within certain limits, by increasing its diametric or propelling area; for in such case the blades will act upon the water more directlythat is, more nearly in a line with or parallel with the shaft. If a screw were placed with its axis at an angle sidewise to the line of movement of the vessel, its action would be the same, excepting that its lifting action upon the vessel would be diminished, and in such case there should be two screws, one upon each side, so that one may counteract the side act-ion of the other.

The above-described method of constructing and arranging screw-propellers, which consists in inclining the shaft and at the same timeincreasing the propelling area of the screw and diminishing its pitch, is particularly applicable to vessels of two or more hulls, as in all such cases the shaft or shafts, if more than one propelleris applied, can pass through the deck, so that the power above the deck can easily be connected with the screw acting below the deck and between the hulls; and by giving the proper inclination to the shaft a screw of larger diameter can be submerged in a small draft of water.

By reference to the accompanying drawings, Fig. 2 shows a plan view of a double-hulled vessel, and Fig. l a section of the same, with the screw-propellers and their shafts seen in elevation. The hulls are represented by A, and the inclined shafts by B and B. These shafts are fixed in proper bearings, G G, on the deck, and are provided with cranks D D, for the direct application of the power. The shaft B is applied near the longitudinal center of the hulls, and has a greater inclination than the shaft B, and, other things being equal, will tend to lift the entire vessel upward with greater force.

Figs. 3 and 4. are side and plan views of a vessel with a screw-propeller, whose shaft is applied at its stern and at a large angle of inclination from the horizon. The engines E E and their connections with the crank-arm of the shaft and the boiler F are shown.

Figs. 5 and 6 are side and plan views of a vessel, showing the application of screw-propellers to the sides of the vessel.

When the shaft is placed at a large angle of inclination from the horizon it is very olesirable to diminish the pitch of the screw as is in a vertical much as practicable, in order to lessen the unequal action of the blades which takes place at difierentparts of their revolution. This inequality of the action of the blades in differentparts of theirrevolution is largely increased by the inclination of the shaft, which causes one of the blades, when their radial length is in a horizontal position, to exert its force more in the direction of the line of movement of the vessel, and the other blade to exert its force at a greater angle to such line of movement. When the radial length of two opposite blades plane, passing through the shaft, the action of each blade upon the water is substantially equal, and the force is exerted in the same direction. If the shaft were very much inclined, with a screwof high pitch, this unequal action of the blades would be quite objectionable; but by diminishing the pitch of the screw as the inclination of the shaft is increased the advantage gained by the lifting thrust far more than compensates the loss arising from the unequal action of the blades.

In order to largely obviate this unequal action of the blades and prevent the tendency to jar the vessel, I prefer to attach the blades to inclined shafts, as shown in Figs. 7, 8, and

9 of Sheet II of the accompanying drawings, by casting or forming the two opposite blades with a round connecting shank or journal, which is secured in a proper hearing formed in the hub and the cap-piece, by which means the screw is attached to the end of the shaft by a hinge-connection at right angles to the line of the shaft. This cross shank or journal is attached to the blades at theirforward edges, so that as they pass through the water the blades will trail behind the hinge, and any excess of pressure upon one of the blades will cause its angle of action to be diminished, and will at the same time increase the angle of action of the opposite blade, and thus automatically equalize their work.

By reference to the drawings, H represents a shaft; I I, screw-blades; J, hub attached to the end. of the shaft; K, shank or journal attached to the forward edges of the blades, as seen in Fig. 7. Misa cap-piece provided with screws, by which it' is firmly secured to the hub, and which serves to hold the shank or journal of the blades in its bearing.

What is claimed as new is The hereinbefore-described improvement in the art of screw propulsion, which consists in placing the screw-shaft on an inclination or angle with the line of movement of the vessel and diminishing the pitch of the screw and increasing its diametric or propelling area according to the inclination or angle of the shaft, and relatively to the pitch and area which the screw would bar e were its shaft horizontal and in the fore-and-aft line of the vessel, substantially as and for the purpose set forth.

JOHN B. ROOT.

Witnesses:

ROBERT H. DUNCAN, BENJ. A. SMITH. 

